Bjørsvik Hans-René, Gambarotti Cristian, Jensen Vidar R, González Raquel Rodríguez
University of Bergen, Department of Chemistry, Allégaten 41, N-5007 Bergen, Norway.
J Org Chem. 2005 Apr 15;70(8):3218-24. doi: 10.1021/jo047919b.
A novel deoxygenation process for N-heteroarene N-oxides is described. The deoxygenation process has been carried out by utilizing some short C-chain alcohols, benzyl alcohol, or 1-phenylethanol as the solvent in the presence of a base, such as sodium alkoxide or sodium hydroxide. A series of N-heteroarene N-oxides was submitted to the developed conditions to provide the corresponding N-heteroarenes with high yield and excellent selectivity. When the deoxygenation is carried out with benzyl alcohol or 1-phenylethanol as the reaction medium, the process can be performed under very mild conditions, at only 30 degrees C. The deoxygenation process is in contrast to several other methods performed without the presence of any transition metal as a catalyst or stoichiometric reagent. DFT calculations suggest that the alkoxide performs a nucleophilic attack on the N-heteroarene in the ortho or para position. This bond is cleaved homolytically with the overall result being that a single electron-transfer step has occurred. The products of this process are an N-heteroarene N-oxide radical anion and an alkoxyl or benzyloxy radical, depending on the solvent that has been used. Successive steps of the mechanism result in an oxygen transfer from the N-oxide to give the deoxygenated N-heteroarene and 1 equiv of the aldehyde, which is the oxidation product of the solvent alcohol.
本文描述了一种用于N-杂芳烃N-氧化物的新型脱氧方法。该脱氧过程是在碱（如醇钠或氢氧化钠）存在下，以一些短碳链醇、苯甲醇或1-苯乙醇为溶剂进行的。一系列N-杂芳烃N-氧化物在优化条件下反应，以高收率和优异的选择性得到相应的N-杂芳烃。当以苯甲醇或1-苯乙醇作为反应介质进行脱氧时，该过程可以在非常温和的条件下进行，仅需30℃。该脱氧过程与其他几种在无任何过渡金属作为催化剂或化学计量试剂的情况下进行的方法不同。密度泛函理论（DFT）计算表明，醇盐对邻位或对位的N-杂芳烃进行亲核进攻。该键发生均裂，总体结果是发生了单电子转移步骤。根据所使用的溶剂不同，该过程的产物是一个N-杂芳烃N-氧化物自由基阴离子和一个烷氧基或苄氧基自由基。该机理的后续步骤导致氧从N-氧化物转移，生成脱氧的N-杂芳烃和1当量对应于溶剂醇氧化产物的醛。
